Flow controls are important in many industries. Whether found on process lines, gas distribution networks, or any system that carries flowing material, flow devices like valve assemblies are vital to regulate material flow within set parameters. Or, in case of problems, the valve assembly can shut-off flow altogether.
Valve assemblies may leverage mechanical mechanisms to regulate this flow. For valve assemblies, these mechanisms may include an actuator, likely pneumatic, that couples with a closure member via a stem. The closure member may embody a plug, a ball, a butterfly valve, and/or like implement that can contact a seat to prevent flow. A sensing mechanism may be useful to monitor the position of the closure member relative to a seat. This sensing mechanism can have a position sensor and a mechanical linkage that couples the position sensor with the stem or other structure that moves in concert with the closure member. In some examples, the actuator includes a pneumatic actuator that converts energy (e.g., compressed air) into mechanical motion to cause the closure member to move between an opened position, a partially opened position, and a closed position.
Valve assemblies may also include computing components that automate operation of the device. These computing components may integrate as part of a controller or “valve positioner.” During operation, the controller receives and processes a control signal from a process control system (also “distributed control system” or “DCS system”). The control signal may define operating parameters for the valve assembly. These operating parameters may set an appropriate flow of material through the valve assembly and into the process line. The controller can translate the operating parameters, often in combination with the output from the position sensor, to regulate instrument gas into the actuator. The instrument gas may pressurize (or de-pressurize) the actuator in a way that moves the valve stem and, in turn, locates the closure member in position relative to the seat to coincide with the operating parameters.